Plate evaporator

ABSTRACT

In a plate evaporator of the falling film type, every second plate interspace constitutes an evaporation space (28) in which evaporation liquid is distributed across the width of the plates in order to run downwardly on the plates, whereas the rest of the plate interspaces constitute condensation spaces (30) for a heat emitting vapor. The invention concerns a particular arrangement for supplying evaporation liquid to the evaporation spaces (28). According to this arrangement, a distribution chamber (27) is delimited within the uppermost part of each plate interspace constituting an evaporation space (28). This distribution chamber extends across the whole width of the plates and communicates with an inlet channel for liquid, extending through the plate package and formed by aligned openings (16) in the plates. In the upper part of each condensation space (30), several sealing means (25) are arranged horizontally spaced from each other. Each sealing means (25) forms together with the two adjacent plates a transferring chamber (29) that is closed from the condensation space (30), but through small holes (17, 18) in the plates communicates with at least one distribution chamber (27) and one evaporation space (28). Heat emitting vapor may flow into each condensation space (30) from above through the gaps formed between the horizontally spaced sealing means (25).

The present invention concerns a plate evaporator of the kind comprisinga package of substantially vertically arranged heat transferring plateswith plate interspaces, every second one of which forms an evaporationspace for at least partial evaporation of a liquid and the rest of theplate interspaces forming condensation spaces for at least partialcondensation of a heat emitting vapour, and further comprising sealingmeans which in the upper parts of those plate interspaces formingevaporation spaces delimit distribution chambers, each of which hasseveral separate connections with at least one evaporation space, theheat transferring plates having through openings forming together aninlet channel for evaporation liquid, which extends through the platepackage and communicates with the distribution chambers.

GB 1.299.481 shows a plate evaporator of this kind, in which heatemitting vapour is transported to the different condensation spaces inthe plate package in the same manner as evaporation liquid istransported to the evaporation spaces, i.e. through a channel formed byaligned openings in the heat transferring plates.

Transportation of heat emitting vapour in this manner through a channelextending through the package of heat transferring plates has severaldisadvantages. One is that the openings in the heat transferring plateshave to be very large for avoiding unnecessary pressure drop of thesupplied vapour, which means that much plate material has to be removedfrom the heat transferring plates. Another disadvantage is that the areaof the vapour inlet to each plate interspace forming a condensationspace becomes relatively small, which creates an undesired pressure dropof the supplied vapour. A third disadvantage is that the pressureconditions at the vapour inlets to the various condensation spaces inthe plate package will become different along the inlet channel throughthe plate package. This results in different temperatures prevailing inthe various condensation spaces, and all of these, therefore, can not beused with the same efficiency.

All of these disadvantages may be avoided if the heat emitting vapour isinstead introduced into the condensation spaces directly from thesurroundings of the plate package through the slots formed between theedge portions of the heat transferring plates.

GB 1.568.733 shows a plate condenser in which the vapour to be condensedis introduced into every second plate interspace through the slotsformed between the edge portions of the plates. In this case the otherplate interspaces form no evaporation spaces but closed passages for acooling liquid. The passages are, thus, closed from the surroundings ofthe plate package by means of gaskets extending along the edges of theplates around the whole periphery thereof.

A main object of the present invention is to provide a plate evaporatorof the initially described kind, in which liquid to be evaporated may bedistributed effectively to the various evaporation spaces in the platepackage as well as within each evaporation space across the whole widthof the heat transferring plates and--simultaneously--the means necessaryfor obtainment of such a liquid distribution does not prevent heatemitting vapour from flowing into the condensation spaces from abovethrough the slots formed between the upper edges of the heattransferring plates.

An object of the invention is also to provide a liquid distributionarrangement that makes it simple and inexpensive to produce plateevaporators of the kind here in question and that makes possible a safeoperation and a simple maintenace service of this kind of plateevaporators.

These objects may be obtained in a plate evaporator of the initiallydefined kind, which is characterized in that at least two sealing meansare arranged in the upper part of each condensation space, horizontallyspaced from each other seen along the heat transferring plates, each ofsaid sealing means delimiting between the heat transferring plates atransferring chamber which is closed from connection with other parts ofthe condensation space, that the condensation spaces communicate withthe surrounding of the plate package through the gaps formed betweensaid sealing means for receiving heat emitting vapour from above, andthat the heat transferring plates have through holes communicating withthe transferring chambers, for each transferring chamber at least onefirst hole connecting the transferring chamber with a distributionchamber and at least one second hole connecting the transferring chamberwith one evaporation space.

It is possible to obtain the above defined objects of the invention ifeach transferring chamber between two heat transferring platescommunicates with a distribution chamber through a hole in one of theheat transferring plates and with an evaporation space through a hole inthe other heat transferring plate. However, according to a preferredembodiment of the invention at least every second heat transferringplate has through holes arranged in pairs, one hole in a pair of holesconnecting a transferring chamber with a distribution chamber and theother hole connecting the same transferring chamber with an evaporationspace.

If desired, each transferring chamber may communicate with two differentdistribution chambers and one or two different evaporation spaces, orwith only one distribution chamber and two different evaporation spaces.

For distribution of liquid to be evaporated across the width of the heattransferring plates in each evaporation space the distribution chamberin every second evaporation plate interspace may--if consideredsuitable--extend across only one half of the width of the heattransferring plates, whereas the distribution chambers in the rest ofthe evaporation plate interspaces extend across the other half of theheat transferring plate width. However, preferably each of thedistribution chambers extends horizontally across the whole width of theheat transferring plates, i.e. between the vertical edge portions of theheat transferring plates, the previously mentioned inlet channel forevaporation liquid extending through the plate package substantially inthe middle between the vertical edge portions.

For obtainment of the smallest possible pressure drop in connection withthe flow of the heat emitting vapour into the condensation spaces thelatter preferably communicate with the surrounding of the plate packagealong the vertical edges as well as along the upper horizontal edges ofthe heat transferring plates.

The invention is described below with reference to the accompanyingdrawing, in which

FIG. 1 shows a container and a plate heat exchanger arranged therein,

FIG. 2 shows a cross-sectional view along the line II--II in FIG. 1,

FIG. 3 shows a cross-sectional view along the line III--III in FIG. 1,

FIG. 4 shows a section through the upper part of a plate heat exchangeraccording to FIG. 1, which section is taken along a line IV--IV in FIG.2 and a corresponding line IV--IV in FIG. 3, and

FIG. 5 shows a flow diagram of a plant for production of fresh waterfrom sea water.

FIG. 6 is a view along the section line VI--VI in FIG. 2.

FIG. 1 shows a closed container 1 in the form of a cylindrical pressurevessel provided with end walls and a plate heat exchanger arrangedwithin the container. The plate heat exchanger comprises two end plates2 and 3 and a package of heat transferring plates 4 which are clampedconventionally between the end plates. The end plates 2, 3 as well asthe heat transferring plates 4 are carried within the container by aframe which is not shown in the drawing, so that they extend vertically.Spacing members, preferably pressed in the heat transferring plates in aconventional manner, keep the heat transferring plates at a distancefrom each other, so that plate interspaces to be flowed through by heatexchange fluids are formed.

A horizontal partition 5 extends within the container 1 all the wayaround the plate heat exchanger, so that it divides the interior of thecontainer in an upper chamber 6 and a lower chamber 7. The upper chamber6 has an inlet 8 for heat emitting vapour and the lower chamber 7 has anoutlet 9 for vapour having been generated in the plate heat exchanger.At its bottom the container 1 has a further outlet 10 from the lowerchamber 7, which is intended for liquid having been supplied to but notbeen evaporated in the plate heat exchanger.

Through one end wall of the container there are extending one pipe 11and two pipes 12, said pipe 11 forming an inlet to the plate heatexchanger for liquid to be evaporated therein, and the pipes 12 formingoutlets for condensate formed in the plate heat exchanger.

Between the heat transferring plates 4 there are arranged sealingmembers of different kinds. These are described below with reference toFIGS. 2 and 3.

FIG. 2 shows one side of a heat transferring plate 4. As can be seen theheat transferring plate has an elongated rectangular form and isarranged in the container 1 such that its long sides extend verticallyand its short sides extend horizontally. The partition 5 extends at acertain level in the container 1 from each of the long sides of the heattransferring plates 4 horizontally towards the surrounding wall of thecontainer 1.

On its side shown in FIG. 2 the heat transferring plate 4 has a firstgasket 13 extending along the edge of the heat transferring plateupwardly from the level of the partition 5 at one long side of theplate, then along the upper short side of the plate and back downwardlyalong the other long side of the plate to the level of the partition 5.As can be seen from FIG. 2, the gasket 13 extends at the long sides ofthe heat transferring plate horizontally up to the respective parts ofthe partition 5.

A second gasket 14 extends in parallel with the upper short side of theheat transferring plate between the vertical portions of the gasket 13,so that an area 15 of the upper part of the heat transferring plate iscompletely surrounded by the gaskets 13 and 14. When the gaskets 13 and14 abut against the plate shown in FIG. 2 as well as an adjacent platein the plate heat exchanger, a closed so called distribution chamberwill be formed in the plate interspace in the area 15, which extendsacross the whole width of the heat transferring plates.

In the area 15 the heat transferring plate 4-like all of the heattransferring plates in the plate heat exchanger-has a through opening16. All of the openings 16 form an inlet channel through the package ofheat transferring plates 4, communicating both with the previouslymentioned inlet 11 (FIG. 1) for liquid to be evaporated and with each ofsaid distribution chambers.

In addition to the opening 16 each heat transferring plate has in thearea 15 and close to the gasket 14 four smaller holes 17 distributedacross the width of the plate. Vertically below each of the holes 17 onthe opposite side of the gasket 14 there is a further small through hole18. Finally, close to the large opening 16 but below the gasket 14 thereare two small through holes 19.

Each heat transferring plate in its lower corner has two through holes20 and 21, which on the plate side shown in FIG. 2 are surrounded by twoannular gaskets 22 and 23, respectively. The holes 20 and 21 in the heattransferring plates form two channels through the plate package, whichcommunicate with the outlets 12 of the plate heat exchanger for liquidhaving been condensed but which are closed by the gaskets 22 and 23,respectively, from connection with the plate interspaces in which thesegaskets are arranged.

FIG. 3 shows one side of a heat transferring plate 4 which is intendedto be placed behind a heat transferring plate according to FIG. 2. Ascan be seen, even the plate in FIG. 3 has in its upper part a relativelylarge opening 16 and substantially smaller holes 17, 18 and 19. Also,the plate in FIG. 3 has through holes 20 and 21 at its lower corners. Inthese respects the plates in FIG. 2 and FIG. 3 are thus alike. The plateaccording to FIG. 3, however, has a different arrangement of gasketsthan the plate according to FIG. 2.

In the upper part of the plate in FIG. 3 the opening 16 and the twosmall holes 19 are surrounded by a first gasket 24. Furthermore, thereare in the upper part of the plate four horizontally spaced gaskets 25.Each of these surrounds a small area of the plate, in which there areboth one hole 17 and one hole 18.

In the lower part of the plate in FIG. 3 a gasket 26 extends along theedge of the plate downwardly from the level of the partition 5 at onelong side of the plate, then along the lower short side of the plate andagain upwardly along the other long side of the plate to the level ofthe partition 5. As can be seen, the gasket 26 extends at the level ofthe partition 5 horizontally up to the respective portions of thepartition 5. The holes 20 and 21 at the lower corners of the plate areplaced inside, i.e. above, the gasket 26.

FIG. 4 shows a section through the upper parts of a number of heattransferring plates, which section is taken along the line IV--IV inFIG. 2 and along a corresponding line IV--IV in FIG. 3.

In every second plate interspace there is shown in FIG. 4 a sectionthrough the upper part of a gasket 13 (FIG. 2) and a section through agasket 14 (FIG. 2). Between the gaskets 13 and 14 there is formed ineach such plate interspace a distribution chamber 27 which extendsacross the whole width of the heat transferring plates 4. Thedistribution chamber 27 communicates with the channel through the platepackage, which is formed by the openings 16 in the plates.

Below the gasket 14 there is formed in each of these plate interspacesan evaporation space 28 in which liquid is to be evaporated. Eachevaporation space 28 is closed from connection with the upper chamber 6in the container 1 by the vertical parts of the gasket 13 (FIG. 2) butcommunicates with the lower chamber 7 in the container 1 through theslots between the edges of the heat transferring plates--along the lowerparts of the plate long sides as well as along the lower short sides ofthe plates. This is illustrated by means of arrows in FIG. 2.

In each of the rest of the plate interspaces there is shown in FIG. 4 asection through a gasket 25 (FIG. 3), which together with the two heattransferring plates against which it seals forms a transferring chamber29. Outside the gasket 25 there is formed in the interspace between thetwo heat transferring plates a condensation space 30. The condensationspace 30 communicates with the upper chamber 6 in the container 1through the slots between the two heat transferring plates along theupper short sides thereof as well as along the upper parts of their longsides. This is illustrated by means of arrows in FIG. 3. Vapour in thechamber 6 thus may flow into each condensation space 30 both from thetwo sides of the plate package and from above through the interspacesbetween adjacent gaskets 25.

Each condensation space 30 is closed by the gasket 26 (FIG. 3) fromconnection with the lower chamber 7 in the container 1.

All of the plate interspaces forming condensation spaces 30, as well asthe upper chamber 6 in the container 1, are closed by the gaskets 24(FIG. 3) from connection with the channel through the plate package,which is formed by the openings 16 in the heat transferring plates.

As illustrated by arrows in FIG. 4, each distribution chamber 27communicates through opposing holes 17 in two adjacent heat transferringplates with two transferring chambers 29. Through opposing holes 18 inthe same heat transferring plates the two said transferring chambers 29communicate with the evaporation space 28 that is formed between the twoheat transferring plates. The holes 18 have somewhat larger throughflowarea than the holes 17.

The apparatus according to FIG. 1-4 is intended to operate in thefollowing manner.

Liquid to be evaporated is pumped in a preheated condition through theinlet pipe 11 (FIG. 1) into the channel through the package of heattransferring plates, that is formed by the openings 16 in the plates.From this channel the liquid flows further out into the differentdistribution chambers 27 (FIG. 4), which extend across the whole widthof the heat transferring plates (see the area 15 in FIG. 2). From thedistribution chambers 27 the liquid flows through the holes 17 in theplates into the various transferring chambers 29 and then through theholes 18 out into the evaporation spaces 28. Simultaneously, liquidflows into the evaporation spaces 28 directly through the holes 19 fromthe plate interspaces in which the gaskets 24 (FIG. 3) surround theopenings 16 and the holes 19. In the evaporation spaces 28 the liquidthen runs downwardly in thin layers along the heat transferring plates,covering the opposing surfaces thereof.

Simultaneously there is supplied to the upper chamber 6 in the container1 through the inlet 8 a heat emitting vapour which flows into thecondensation spaces 30 through the slots between the edges of the heattransferring plates, as illustrated in FIG. 3. The heat emitting vapourcondensates in the condensation spaces 30 upon its contact with the heattransferring plates to which it thus emits heat. This heat causesevaporation of the liquid running downwardly along the opposite sides ofthe plates in the evaporation spaces 28. Vapour formed in theevaporation spaces 28 leaves and flows out into the lower chamber 7 ofthe container 1 both sidewise and downwardly, as illustrated by means ofarrows in FIG. 2. The generated vapour leaves the chamber 7 through theoutlet 9, whereas unevaporated liquid is collected at the bottom of thecontainer and is discharged--continuously or intermittently--through thebottom outlet 10 (FIG. 1).

Condensate formed by the heat emitting vapour in the condensation spaces20 runs downwardly along the heat transferring plates and leaves thecondensation spaces through the two channels formed by the holes 20 and21 in the lower parts of the heat transferring plates. These channelsare closed from communication with the evaporation spaces 28 by thegaskets 22 and 23 (FIG. 2). Even uncondensed parts of the heat emittingvapour leave the condensation spaces 30 through said channels and isdischarged together with the condensate through the outlets 12 (FIG. 1).

As mentioned previously, the holes 18 are somewhat larger than the holes17. The hole sizes are chosen such that during the operation of theapparatus a partial evaporation of evaporation liquid is obtained whenthe liquid passes through the holes 17. The holes 18 are made largeenough so that the vapour pressure that will prevail in the transferringchambers 29 shall not exceed the vapour pressure prevailing in the heatemitting vapour in the condensation spaces 30. The purpose thereof is toguarantee that upon possible leakage past the gaskets 25 such leakageshall be directed into the transferring chambers 29 and not out of thesechambers. Particularly if the apparatus according to the invention isused for the production of fresh water from for instance sea water, itis better if vapour flows into the sea water than if sea water flowsinto the fresh water.

In the embodiment of the heat transferring plates 4 shown in FIGS. 2 and3 each plate has holes 17-19 on both sides (both to the left and to theright) of the opening 16. If desired, the holes 17-19 may be excluded inevery second plate on one side of the opening 16 and in the rest of theplates on the other side of their openings 16. Alternatively, the holes17 may be excluded in every second plate on one side of the opening 16,and the holes 18 and 19 may be excluded on the other side of the opening16, whereas in each of the rest of the plates the holes 17 may beexcluded on said other side and the holes 18 and 19 be excluded on saidone side of the opening 16. Even in these cases liquid will bedistributed across the whole width of the plates in each of theevaporation spaces 28.

It has been assumed above that the sealing members arranged between theheat transferring plates are constituted by elastic rubber or plasticgaskets of the kind usually used in connection with heat transferringplates of thin pressed metal sheet. Of course, any other suitable kindsof sealing members may be used. As sealing means could also be chosenpermanent interconnection of the heat transferring plates along thelines which in FIGS. 2 and 3 show how different gaskets are extending.The heat transferring plates may be pressed in a way such that they abutagainst each other along these lines in the respective plateinterspaces, so that sealing between--possibly interconnection of--theplates is facilitated.

Thanks to the design of the above described apparatus the smallestpossible pressure drop is obtained for the working vapours at theirentering into and discharge from, respectively, the plate heatexchanger. This makes the apparatus effective and inexpensive inoperation.

FIG. 5 shows a flow diagram of a plant in which the described apparatusis included. The plant is intended for the production of fresh waterfrom sea water. Thus, FIG. 5 shows the container 1 with its inlet 8 forheat emitting vapour, its inlet 11 for liquid to be evaporated, i.e. seawater, its outlet 9 for generated vapour, its outlet 10 for concentratedliquid, i.e. sea water having not been evaporated, so called brine, andits outlet 12 for condensate, i.e. fresh water, and uncondensed parts ofthe heat emitting vapour.

Sea water is pumped by means of a pump 31 into the plant. After the pump31 the sea water is divided at 32 in two branch flows. One passesthrough a heat exchanger 33 and the other through a heat exchanger 34.The branch flows are then united at 35 and are pumped furtheron throughanother heat exchanger 36 to the inlet 11 of the container 1. Thegenerated vapour leaving the container through the outlet 9 istransferred through a compressor 37 to the inlet 8 for heat emittingvapour. A conventional high pressure fan may serve as a compressor.

So called brine, i.e. sea water having not been evaporated in thecontainer 1, is pumped by means of a pump 38 out of the container 1through its bottom outlet 10 and is divided at 39 in two branch flows.One branch flow is returned to the container inlet 11 for liquid to beevaporated, whereas the other branch flow is pumped by means of a pump40 through the heat exchanger 33 and out of the plant. In the heatexchanger 33 this branch flow emits part of its heat to one of thebranch flows of incoming sea water.

A mixture of fresh water, i.e. condensate from the heat emitting vapoursupplied through the inlet 8, and non-condensed residuals of this vapourare removed from the container 1 through the outlet 12. In a separator41 the gaseous parts of the mixture are separated, and by means of avacuum pump 42 they are sucked through the heat exchanger 36 and out ofthe plant. In the heat exchanger 36 they emit part of their heat to thealready partly preheated incoming sea water.

The fresh water is pumped from the separator 41 by means of a pump 42through the heat exchanger 34 and out of the plant. In the heatexchanger 34 the fresh water emits part of its heat to a branch flow ofthe incoming sea water.

In the described plant the incoming sea water preferably is preheatedalmost to a temperature corresponding to its boiling point at theevaporation pressure to be prevailing in the evaporation spaces of theplate heat exchanger. For instance, the sea water may be preheated sothat it has a temperature of 55° C. in the container inlet 11. Thegenerated vapour in the container outlet 9 may have a temperature onlyinsignificantly exceeding 55° C. and a pressure of for instance 0,15bars. The vapour may after that be compressed to having in the containerinlet 8 and in the chamber 6 a pressure of about 0,19 bars and atemperature of about 59° C.

We claim:
 1. Plate evaporator comprising a package of substantiallyvertically arranged heat transferring plates (4) with plate interspaces,every second one of which forms an evaporation space (28) for at leastpartial evaporation of a liquid and the other plate interspaces formingcondensation spaces (30) for at least partial condensation of a heatemitting vapour, and further comprising first sealing means (13, 14)which in an upper part of the plate interspaces forming evaporationspaces (28) delimit distribution chambers (27), each of which hasseveral separate connections with at least one evaporation space (28),the heat transferring plates (4) having through openings (16) forming aninlet channel for evaporation liquid, which extends through the platepackage and communicates with the distribution chambers (27), whereinatleast two second sealing means (25) are arranged in an upper part ofeach condensation space (30), horizontally spaced from each other alongthe heat transferring plates (4), each of said second sealing meansdelimiting between the heat transferring plates (4) a transferringchamber (29) that is closed from connection with other parts of thecondensation space (30), the condensation spaces (30) communicate withthe surrounding of the plate package through the gaps formed betweensaid second sealing means (25) for receiving heat emitting vapour fromabove, and the heat transferring plates (4) have through holes (17, 18)communicating with the transferring chambers, for each transferringchamber (29) at least one first hole (17) connecting the transferringchamber (29) with a distribution chamber (27) and at least one secondhole (18) connecting the transferring chamber (29) with an evaporationspace (28).
 2. Plate evaporator according to claim 1, wherein at leastevery second heat transferring plate (4) has said through holes (17, 18)arranged in pairs, said first hole (17) in a pair of holes connecting atransferring chamber (29) with a distribution chamber (27) and saidsecond hole (18) connecting the same transferring chamber (29) with anevaporation space (28).
 3. Plate evaporator according to claim 1,wherein each heat transferring plate (4) has vertical and horizontaledge portions, each of the distribution chambers (27) extendshorizontally between the vertical edge portions of the heat transferringplates and the inlet channel for evaporation liquid extends through theplate package substantially in the middle between said edge portions. 4.Plate evaporator according to claim 1, wherein each heat transferringplate (4) has vertical and horizontal edge portions, and thecondensation spaces (30) communicate directly with the surrounding ofthe plate package along the vertical as well as the upper horizontaledges of the heat transferring plates.
 5. Plate evaporator according toclaim 1, wherein said first hole (17) is smaller than said second hole(18).